2 Column "Moment" Base Plate

[ToadJones]

I have a large base plate with two columns landing on it.
The columns are laced together making up one big section.
It is essentially a moment base, but the moment is really just resisted by a couple in the columns and not in the base plate itself.
The base plate is loose, not welded to the column. Uplift is taken by brackets on the columns.

So I have uplift on one column at one end of the base plate and a downward force at the other.
The columns are six feet apart.

Do you think it is reasonable to analyze the plate using a "concentric" area around the column and a typical base plate analysis?

 

[ishvaaag]

It could be reasonable enough, I think; considering the influence of distance to neutral axis for the moment would be even more safe, describing bigger reacting stresses.

 

[slickdeals]

I guess it's no different than having a braced frame, right?

 

[ToadJones]

slick-
that's basically the way i see it.

My question, however, is with regard to ignoring the portion of the base plate outside the area concentric to the compression column.

I think this approach is conservative, just wondering what others think.

 

[paddingtongreen]

I think I would bracket the solution by:
1. Taking the concentric assumption.
2. Considering the base plate as rigid and the concrete as springs. Load may be out of the middle third.
The real analysis is somewhere between these so design for both of these.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[Lion06]

I think you're fine using that approach. One of the methods AISC gives in the Baseplate Design Guide for analyzing existing baseplates is to use just enough area of baseplate to make the bearing stresses work out on the support. That decreases the cantilever distance of the plate and makes it a lot happier.

 

[Ron]

I see nothing wrong with your approach...after all, suppose you took a torch and cut the baseplate between the columns. It would not change the global parameters of your baseplate, the columns or your load response.

 

[ToadJones]

Ron-
I will have the guys torch the plate, run my numbers, then weld the plate back together!

I kid

Thanks for the responses, I appreciate it.

 

[BAretired]

Toad,

You could have saved material by using two base plates. I agree with the others. If a small baseplate works, it cannot be made more critical by enlarging its area.

BA

 

[Ron]

TJ...make sure the welder is certified!

 

[ToadJones]

BA-
Existing structure.